This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Phytochromes comprise a principal family of red/far-red light sensors in plants. We will attempt structure determination of two new thermostable cyanobacterial phytochromes (comprising the domain which houses the chromophore - phycocyanobilin). This construct photoconverts and is only 23.6 kDa and we would like to also determine its Pr andf Pfr forms upon red light exposure.On the long run we would like to eventually determine homodimer structures of these domains and the complexes with PHY signaling domains.